Carbon nanotubes (CNTs) have been identified as fundamentally new nanoporous materials that show great potential for sensors,1, 2 composites,3 catalytic supports,4 and as membrane materials.5, 6 In particular, CNTs, which may have an inner core diameter as small as 4 Å7, 8 have been earmarked as possible selective nanopores in membrane materials.9, 10
Previous studies by Hunt et al.6 have shown that Si3N4 composite membranes with aligned double walled carbon nanotubes (DWNT) having a diameter of about 1.6 nm show gas flow through that is one to two orders of magnitude faster than that obtained with a commercial polycarbonate nanoporous membrane having 15 nm pore size. These studies have also found that liquid water flow through these nanotube membranes was more than three orders of magnitude faster than expected from hydrodynamic flow calculations. Moreover, these nanotube membranes exhibited extraordinarily high size exclusion selectivity. In related work, Hinds et al.5 constructed polymer-nanotube composite membranes using multiwalled carbon nanotubes (MWNT) having large diameters (6-7 nm). Further study of these composite membranes verified that transport of liquids (alkanes, water) is orders of magnitude faster than can be accounted for by conventional hydrodynamic flow.14 
Although composite membranes made with DMNTs and MWNTs have shown promising results, the use of single-walled nanotubes (SWNTs) for forming membranes is particularly intriguing. Recently, computer simulations have been used to investigate the adsorption,30-34 selectivity,35-37 and transport properties9,10 of light gases in SWNTs. Johnson et al. have identified single walled carbon nanotubes as a fundamentally new nanoporous material that shows great potential for membrane materials.9,10 That group reported transport rates in nanotubes to be orders of magnitude faster than in zeolites and demonstrated that the exceptionally high transport rates are a result of the inherent smoothness of the nanotubes.
In addition to allowing the fast transport rates afforded by all CNTs, SWNTs are smaller diameter carbon nanotubes with 4 to 12 Å pore openings in a size range that may allow for size-selection of gas mixtures. Recent computer simulation work by Sholl et al. has shown that SWNT membranes should be strongly selective for CH4 over H2 and should have flux/selectivity properties that far exceed those of any other known inorganic materials.13 
In order for SWNTs to effectively act as channels in a membrane, however, they must to be aligned correctly relative to the penetrant stream. This alignment is perhaps the single most important challenge facing the fabrication of SWNT membranes.
Chemical vapor deposition has been used to grow oriented carbon nanotubes.5, 6 While chemical vapor deposition produces well-aligned carbon nanotubes, the process is expensive, tedious and is limited to fabricating samples with small surface areas (e.g. sub cm2). In an alternative approach, CNTs have been aligned by employing filtration methods.15, 16 However, to date, filtration has been successful only with MWNTs.
As such, there remains a need in the art for a method for an facile, efficient and inexpensive manner for forming composite membranes with aligned CNTs, especially SWNTs.